feat(db): add versioned habits and calendar domain contracts

src/habits/calendar.ts

@@ -0,0 +1,39 @@
+import type { Schedule, CalendarSettings } from './contracts';
+const DAY = 86400000;
+export const dayNumber = (date: string) => Date.parse(`${date}T00:00:00Z`) / DAY;
+export const addDays = (date: string, n: number) => new Date((dayNumber(date) + n) * DAY).toISOString().slice(0, 10);
+export function localDate(timestamp: number, timezone: string): string {
+  return new Intl.DateTimeFormat('en-CA', { timeZone: timezone, year: 'numeric', month: '2-digit', day: '2-digit' }).format(timestamp);
+}
+// Search an instant boundary rather than adding 24h: DST days can be 23 or 25h.
+export function endOfDay(date: string, timezone: string): number {
+  const target = addDays(date, 1);
+  let lo = Date.parse(`${target}T00:00:00Z`) - 36 * 3600000;
+  let hi = lo + 72 * 3600000;
+  while (hi - lo > 1) {
+    const mid = Math.floor((lo + hi) / 2);
+    if (localDate(mid, timezone) < target) lo = mid; else hi = mid;
+  }
+  return hi;
+}
+export function scheduled(rule: Schedule, date: string): boolean {
+  const day = dayNumber(date);
+  const weekday = new Date(day * DAY).getUTCDay();
+  if (rule.type === 'daily') return true;
+  if (rule.type === 'weekdays') return rule.days.includes(weekday);
+  const anchor = dayNumber(rule.anchor);
+  if (day < anchor) return false;
+  if (rule.type === 'interval') return (day - anchor) % rule.every === 0;
+  // Weeks start Monday; the anchor identifies week zero, even if not the due weekday.
+  const monday = (n: number) => n - ((new Date(n * DAY).getUTCDay() + 6) % 7);
+  return weekday === rule.weekday && (monday(day) - monday(anchor)) / 7 % rule.every === 0;
+}
+export function shade(ratio: number | null, steps: number, settings: CalendarSettings, exactSteps: boolean) {
+  if (ratio === null) return { level: null, color: settings.notDueColor };
+  if (ratio <= 0) return { level: 0, color: settings.emptyColor };
+  const total = exactSteps ? steps : settings.shadeCount;
+  const level = exactSteps ? Math.min(total, Math.round(ratio * total)) : ratio >= 1 ? total : Math.min(total - (total > 1 ? 1 : 0), Math.max(1, Math.floor(ratio * total)));
+  const intensity = total <= 1 ? 1 : 0.2 + 0.8 * (level - 1) / (total - 1);
+  const color = '#' + [1, 3, 5].map(i => Math.round(255 * (1 - intensity) + parseInt(settings.mainColor.slice(i, i + 2), 16) * intensity).toString(16).padStart(2, '0')).join('');
+  return { level, color };
+}